Problems with cascade level and flow control
Thread Content
This is a set of laboratory equipment for schools. Water enters the tank through a pump and an electric actuator; a ball valve is used for manual control when water enters the tank, and another ball valve is used for manual control when water exits. According to the experimental requirements, the water inflow rate serves as the secondary control parameter, while the tank’s liquid level functions as the primary control parameter. Question 1: My idea is to first connect all the wires related to the regulator, actuator, and electromagnetic flow meter. Then power it on; open the manual inlet ball valve fully and open the outlet ball valve to 75%. Set the main level control at P 30, I 50, D 0. For the secondary control, set it at P 50, I 2000 (the instructor said that the secondary control should be purely proportional, so I chose the maximum value). Next, use the manual control of the secondary control to activate the electric actuator. For the inlet flow, if the target value is set at 200, use the electric actuator to adjust it to around 200 before switching to automatic mode. Due to the time limit of only half an hour, it is not possible to adjust the PID by first dealing with the secondary parameters and then the primary ones. Only the fixed sub-tone and main tone – just enter a number and it’s set. . . Also, at the initial stage of water intake, should it be set to automatic mode so that the water level rises to around 200 on its own, with the system then monitoring that level and adjusting the PID? Is that method more standard and saves more time? Question 2: Regarding the PID issue… In the regulator’s specifications, it is stated that a larger value of P results in smaller fluctuations, while too small a value leads to oscillations and divergence. Does this P refer to the proportional band or the proportional gain? ? ? ? I looked at the mnemonic, but still couldn’t figure out the pattern. . I know I need to try it on my own, but I don’t have the time for training. . Damn this school – it doesn’t give us much time to practice, and exams are coming up already. Final exams are near. . I’m very worried. . . Thank you to all the teachers. . . . Haichuan Chemicals Forum-20150513_151509.jpg (27.66 KB, Downloads: 0) Entire Haichuan Chemicals Forum-20150513_152034.jpg (23.33 KB, Downloads: 0) Using just 2 regulators Haichuan Chemicals Forum-20150513_152129.jpg (25.14 KB, Downloads: 0) Below
This post was last edited by ylb913 on 2015-6-23 at 23:00. I only read part of it; please forgive me. I think it should be filled with water first, to the amount you mentioned, 200 – whatever unit that is. No experiments have been conducted; it’s only for industrial use. For PID control, initial values are set according to conventional methods. It would be good if there are predetermined values as well, but I don’t know how to calculate the speed at which this control works. It has to be determined through practical experimentation with each relevant valve, though most valves don’t require any special attention. In industrial applications, they are generally manual at the beginning as well. When should it be set to automatic? Without going into too much detail, regarding your situation, there are two points of concern: 1. The most problematic aspect is the lack of a concept of volume; after filling the tank with water, if the drainage isn’t turned on and the filling valve is closed, and the valves don’t leak, then nothing should happen and the liquid level should remain stable. 2. What is the relationship between the main circuit and the auxiliary circuit? It’s a bit messy; let me organize it: one tank, with flow control at the inlet and level control at the outlet. In such cases, the flow rate is fixed, while the liquid level is variable. By \"fixed\" it doesn’t necessarily mean an absolute constant value; it also refers to the amount of fluid that enters and the amount that is collected. It’s still chaotic. Let’s take an example of an industrial application: the incoming flow rate is not under control; there is only a display of the flow rate. The outgoing flow rate is determined through a cascade control system based on both the flow rate and the liquid level. Of course, the priority here is to consider the liquid level, using changes in the liquid level to adjust the set value for the outgoing flow rate, with the ultimate goal being to maintain relative stability in the outgoing flow rate. The key issue is that two parameters are used to control a valve. 3. The topic is how to adjust the PID, which is related to flow rate, that is, to the opening degree of the valve. At different opening degrees, the regulation performance of the valve varies. ——After thinking for a long time, this isn’t what is commonly referred to as instrument cascade control. ——Are you trying to get things stabilized as quickly as possible? Should we still examine the impact of different PID parameter settings?
200 is in mm; this represents a cascade control system for the inflow rate and liquid level. . . Manual ball valve, one for water inlet and one for water outlet. . . In addition to the manual ball valve, the water inlet is also controlled by an electric actuator; there is an electromagnetic flow meter on the water inlet pipeline as well. It’s this entire set of equipment